A variety of trenchless excavation technologies have been developed to increase installation efficiency of various underground utilities. Horizontal direction drilling (HDD), for example, is increasingly being used for utility line installations. Other popular trenchless excavation technologies include percussive moles and plowing. Trenchless excavation technologies have the advantage of not being disruptive to the surface, yards, roads, driveways, traffic, and trees, for example, but have the disadvantage of not allowing installers to see with their own eyes where utility lines are being installed.
A particularly concerning situation arises when a new utility is to be installed in a subsurface where an existing underground utility is located. In this scenario, a cross bore may arise. A cross bore is generally understood in the industry as an intersection of an existing underground utility or underground structure by a second utility resulting in direct contact between the transactions of the utilities that can compromise the integrity of either utility or underground structure.
By way of example, it sometimes occurs that a utility installation contractor using an HDD machine to install a gas service line inadvertently drills through or very near a main sewer or sewer lateral pipe and unknowingly installs a gas supply pipeline through or in contact with the sewer pipe. This direct or proximal unintended contact between underground utilities represents a cross bore. At some later date when a back-up occurs in the sewer, the owner might engage a sewer cleaner using a cutter device to clear the sewer. This can lead to a breach in the gas line and subsequent ignition of gas which flows into the sewer line.
It can be appreciated that installing new utilities within a subsurface that includes legacy utilities is problematic in cases where the location, size, orientation, type, material, and other characteristics of such legacy utilities are either uncertain or unknown. Sewer authorities may complain that newly constructed sewer lines are being damaged when underground utility lines are installed and utility installers may complain that sewers are not properly located or their locations are not accurately documented.
In view of the thousands of miles of sewers situated where utility lines have been installed with trenchless technologies, there may exist a legacy of thousands of cross bores of gas supply pipelines alone in sewers. In addition to gas explosion concerns, damage done to existing utilities due to cross bores is dramatic. For example, holes broken into sewers increases infiltration and inflow of water into sewers, creating structural deficiencies that may eventually create sinkholes and voids that may be extremely expensive to repair.